1,3-propanediol (PDO) is a compound having multiple uses. It is used as a monomer unit in the production of polyesters and polyurethanes that are useful as films and as fibers for carpets and textiles. It is also useful as an engine coolant.
PDO may be prepared from ethylene oxide (EO) in a process involving two primary reactions. First, EO and synthesis gas (H2/CO) are catalytically hydroformylated to form 3-hydroxypropionaldehyde (HPA) in an organic solvent. The HPA is extracted from the solvent with water to form an aqueous solution of HPA, and the aqueous solution of HPA is then hydrogenated to form PDO.
The hydrogenation of HPA to PDO is performed using a hydrogenation catalyst. The hydrogenation catalyst should desirably have several features: 1) it should be highly active over an extended period of time; 2) it should cause the hydrogenation to be highly selective to the formation of PDO, rather than other compounds; 3) it should have a long catalyst life; 4) it should not be discharged into the PDO product stream; and 5) it should be economically cost effective, preferably using inexpensive components and, if required, as few expensive components as possible.
According to Hatch et al., U.S. Pat. No. 2,434,110, especially preferred catalysts for hydrogenating HPA to PDO are Raney nickel and Adkin's copper-chromium oxide. Hatch et al. also disclose that other suitable catalysts for hydrogenating HPA to PDO include catalytically active compounds of metals such as Fe, Co, Cu, Pd, Zr, Ti, Th, V, Ta, Ag, Mo, and Al. Slurry catalysts such as Raney nickel are known to have high activity and selectivity in converting HPA to PDO as a result of the homogeneous distribution of the catalyst in the hydrogenation reaction mixture. Suspended or slurry catalysts, such as Raney nickel, however, are susceptible to being discharged into the PDO product stream in the form of soluble compounds, necessitating additional steps to purify the PDO product stream.
Haas et al., U.S. Pat. No. 6,232,511, discloses that a supported ruthenium catalyst is useful in the hydrogenation of HPA to PDO, and avoids the problem of the metallic portion of the catalyst polluting the PDO product stream. Use of the supported ruthenium catalyst in a fixed-bed is preferred. Ruthenium and other noble metals such as platinum or palladium, however, are very expensive, and ruthenium and other noble metal based catalysts are not commercially attractive, especially for large scale continuous operations.
Arhancet et al. U.S. Pat. Nos. 5,945,570 and 6,342,464, disclose a hydrogenation catalyst for hydrogenating HPA to PDO that is a bulk metal catalyst. The bulk metal catalyst includes 25 to 60 wt. % nickel and 5 to 20 wt. % molybdenum bound together with a binder made up of oxides of silicon, and silicates and oxides of zinc, zirconium, calcium, magnesium and/or aluminum. The catalyst is particulate and may be used in a fixed bed hydrogenation reactor such as a trickle bed reactor. Bulk metal catalysts, however, are subject to breaking into catalytic fines over an extended period of use, and may lack sufficient physical stability to be used in large scale long-term continuous operations.
In short, hydrogenation catalysts in the art formed of economically advantageous non-noble catalytic metals either do not exhibit sufficient hydrogenation activity over an extended period of time, are discharged into the product stream requiring additional steps to purify the product stream, or are not sufficiently physically stable to be utilized in an industrial scale continuous long-term aldehyde hydrogenation process.